For example, when contacts of an electronic component such as an electrical connector and lead frame are electrically connected to circuit terminals of a wiring substrate, it is common to connect terminal portions of the contacts to the wiring substrate by soldering.
The contacts described above are usually formed by punching, bending, or the like from a metal plate, and their conductive basis material consists of a contact portion, an intermediate portion and a terminal portion and is plated with conductive metals suitable for the respective portions of the basis material.
For example, in general, the surface of the contact portion of the basis material is plated for electrical contact in consideration of corrosion resistance, conductive property and the like, while the terminal portion formed contiguously to the contact portion is plated with a metal suitable for subsequent soldering (referred to hereinafter as “plating for soldering”) in order to perform soldering (jointing) securely and effectively in a post-process, in other words to cause the terminal portion to have affinity (wetting) with the solder.
The plating for soldering is usually solder plating, but there may be gold (Au) plating, palladium (Pd)-nickel (Ni) plating, palladium plating, tin (Sn) plating, and the like.
By the way, when the terminal portion of a contact is jointed to a substrate by soldering, there is often a tendency to cause problems that molten solder on the side of the substrate or molten solder of solder plating applied to the terminal portion itself would rise or climb up under a wetting condition beyond the position of the terminal portion of the contact all the way to the contact portion of the contact with the aid of capillary action due to a shape of the contact, and the molten solder would flow so as to contaminate the contact portion.
In order to prevent the solder from rising, certain methods have been employed, for example, in that a tape is used for masking a portion of a contact plated with nickel which requires a barrier for the nickel plating layer, or a resin or the like is used for mechanically masking a portion of the nickel plated layer where a barrier is required and the plating is effected.
However, the former method requires a tape having some width so that this method is not suitable for the microcontact according to the invention needing to form an extremely narrow barrier for the nickel plating layer. In addition, a particular tape has to be used in the former method so that a manufacturing cost would go up.
Moreover, the latter method must necessarily make a mechanical mask for each product. Therefore, in addition to increase in production cost, positional control between the contact and the mask must be precisely carried out so that it becomes difficult to increase the speed of plating to provide a new problem to be solved.
As a further method for preventing the solder from rising due to wetting, there is, for example, a method disclosed in patent literature 1 proposed by the applicant of the present application and opened, this disclosure clarifying that it is useful to provide a nickel oxide layer in the intermediate portion positioned between a contact portion and a terminal portion. According to the method for forming a nickel oxide layer described in the patent literature 1, after a nickel layer has been provided as a base plating layer, the contact portion is plated as plating for electric contact and the terminal portion is plated as plating for soldering, providing a predetermined spacing (practically in the order of 0.3 to 2.8 mm) therebetween, and thereafter oxidation treatment of the nickel layer exposed between the contact portion and the terminal portion is carried out to form a nickel oxide layer.    Patent Literature 1: Japanese Patent Application Opened No. H10-247,535 (1998).
With the method for forming the nickel oxide layer described in the patent literature 1, however, the plating for electrical contact and plating for soldering must be carried out while the nickel layer is exposed with the predetermined spacing. Particularly, setting or positioning with a high accuracy is required for forming a nickel oxide layer with a high accuracy on a microcontact having a width less than 5 mm at the intermediate portion so that there is a tendency for equipment cost to be increased. Further the method disclosed in the patent literature 1 requires an additional independent process for oxidizing the nickel layer.